1. Medawar, P. B. An Unsolved Problem of Biology (Lewis, London, 1952).
2. Williams, G. C. Evolution 11, 398–411 (1957).
3. Charlesworth, B. Evolution in Age-structured Populations (Cambridge Univ. Press, Cambridge, 1980).
4. Rose, M. R. The Evolutionary Biology of Aging (Oxford Univ. Press, Oxford, 1991).
5. Partridge, L. & Barton, N. H. Nature 362, 305–311 (1993).